The present invention relates to radio-frequency identification (RFID) systems, including RFID tags and readers. The invention also relates to RFID apparatus and methodology that enables a plurality of cartons, such as stacked on a pallet, to be read—even the innermost cartons in the stack and even in the presence of RF intolerant material such as liquids and metals.
Automatic identification is the broad term applying to a host of technologies that are used to help machines identify objects. Automatic identification is often coupled with automatic data capture. More specifically, companies want to identify items, to capture information about the items, and to load the information into a computer with minimal human labor.
One type of automatic identification technology is radio-frequency identification (RFID). RFID is a generic term for technologies that use radio waves to automatically identify individual items. There are several conventional methods of identifying objects using RFID, the most common of which is to store a serial number (and other information if desired) that identifies a product on a microchip that is attached to an antenna. The chip and the antenna together are called an RFID transponder or an RFID tag. The antenna enables the chip to receive commands from and to transmit identification information to a reader. The reader converts the radio waves returned from the RFID tag into a form that can then be utilized by a computer.
Accordingly, a conventional RFID system consists of a tag (including a chip with an antenna) and a reader (sometimes call an interrogator) with an antenna. The reader sends out electromagnetic waves that form a magnetic field when coupled with the antenna on the RFID tag. A passive RFID tag draws power from this magnetic field and uses the power to drive or activate the chip. The chip then modulates the waves that are sent back to the reader, and the reader converts the returned waves into digital data.
There are generally two types of RFID tags: active and passive. An active RFID tag utilizes a battery to power the chip and to transmit a signal to a reader (similar to a cell phone transmitting signals). A passive tag does not have a battery but rather is powered by the electromagnetic waves that induce a current in the antenna of the tag. A semi-passive tag uses a battery to power the chip but communicates using electromagnetic waves from the reader.
Similar to an audio radio tuning in to different frequencies, RFID tags and readers are tuned to the same frequency to communicate. RFID systems use many different frequencies, but the most common frequency ranges utilized in RFID systems are low-frequency (about 125 KHz), high-frequency (13.56 MHz), and ultra-high frequency or UHF (about 900 MHz). Microwaves, which have a frequency of about 2.45 GHz, are also used in some applications.
The distance at which an RFID tag can be read is known as the read range. The read range of a passive tag depends on a number of factors: the frequency of operation, the power of the reader, and interference from metal objects or other RF devices. In general, low-frequency tags have a read range of about one foot; high-frequency tags have a read range of about three feet; and UHF tags have a read range of about 20 feet. Where longer read ranges are needed, an active tag with a read range of 300 feet or more can be used.
One of the desired applications of RFID tags is to track goods in a supply chain, particularly at high volumes such as a plurality of cartons stacked on a pallet. One of the inherent difficulties in this application is ensuring that all of the RFID tags associated with all of the cartons are read. For example, if the stack of cartons is a five-by-five layer stacked five layers high (i.e., 125 cartons total), then the user would want to ensure that all 125 RFID tags are read, even those tags mounted to cartons located in the center of the stack. This effectiveness of this operation may be aggravated by the presence of material that is not conducive to RF reading.
More specifically, radio waves are able to travel through most non-metallic materials, so that RFID tags can be embedded in packaging or encased in protective plastic for weather-proofing and durability while still being readable. However, radio waves reflect off metal and are absorbed by water and complex organic molecules such as fat at higher frequencies. These characteristics make tracking metal products or those with high water content problematic. In addition, reading a stack of cartons with RFID tags, particularly cartons located in the center of the stack or cartons that may contain metals or liquids, is also problematic.
In view of the foregoing, there is a need in the art for RFID technology that enables all of the RFID tags in a stack of cartons to be read. The present invention satisfies this need.